Polishing liquid for components, preferably wafers, process for producing polishing liquid and process for chemical mechanical polishing of components

ABSTRACT

A polishing liquid for components, preferably wafers, a process for producing a polishing liquid and a process for chemical mechanical polishing of components are provided. The polishing liquid has a polishing base liquid and an oxidizing agent. The aim is to provide an economical polishing agent which is also simple to produce, which can be used as an alkaline or acidic polishing agent and with which metallic layers in particular can be polished. Ozone, which is used as an oxidizing agent, is a strong oxidizing agent having a redox potential that is sufficient for oxidizing or polishing the metals in an acidic or alkaline environment.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending InternationalApplication No. PCT/DE99/02959, filed Sep. 16, 1999, which designatedthe United States.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a polishing liquid for polishingcomponents, preferably wafers, in particular for chemical mechanicalpolishing of components of this type, having a base polishing liquid andan oxidizing agent. The invention also relates to a process forproducing a polishing liquid of this type and to processes for using apolishing liquid of this type.

[0004] In the semiconductor industry, the ever decreasing size ofstructures leads to increasingly high demands being imposed on theplanarity of the surfaces of components which are to be machined. Oneexample of a conventional process for producing planar surfaces ischemical mechanical polishing (CMP). In this process, certain materialsare abraded over previously patterned areas through the use of anabrasive-containing polishing liquid (also known as a slurry).

[0005] Particularly if metal layers are being polished, an oxidizingagent has to be added to the polishing liquids. As a result, the surfaceis chemically etched and the metal surface which has now been oxidizedcan be mechanically abraded or is dissolved. Oxidizing agents thereforeallow controlled abrasion of metal at a sufficiently high rate.

[0006] Heretofore, either hydrogen peroxide (H₂O₂)or salts of elementsof a high oxidation number (e.g. Fe(III), Ce(IV), (S₂O₈)²⁻) have beenused as oxidizing agents. However, these substances have a number ofdrawbacks with a view to simple handling under production conditions.

[0007] Hydrogen peroxide is unstable, its decomposition beingaccelerated in the presence of extremely small metal impurities or bythe action of light. This makes it more difficult, or under certaincircumstances impossible, for the polishing apparatus to be continuouslysupplied with a polishing liquid of constant H₂O₂ concentration (inparticular when a central chemical supply system is being used). Addingthe polishing liquid in the immediate vicinity of the component which isto be polished (point of use), as is sensible in view of the instabilityof the peroxide, requires installations for mixing and storing liquid inthe immediate vicinity of the production installations. However, thissolution is not always desirable for various reasons.

[0008] The addition of solids, such as salts or the like, is often morecomplex than the addition of liquids, and the solubility of these solidsis often pH-dependent. For example, in a neutral and alkaline medium,metals form hydroxides of low solubility which are deposited in thepolishing apparatus and in feedlines, so that additional cleaningmeasures are required.

[0009] Therefore, for the above reasons the use of heavy metal salts(such as, for example, Fe(III) nitrate, ammonium cerium (IV) nitrate) isrestricted to acidic polishing liquids. It is not possible to usealkaline polishing media, which may have better properties, for examplewith regard to stability, selectivity, mechanical abrasion or the like.Moreover, the metal-containing waste waters have to be disposed of.

SUMMARY OF THE INVENTION

[0010] It is accordingly an object of the invention to provide apolishing liquid for components, preferably wafers, a process forproducing a polishing liquid and a process for chemical mechanicalpolishing of components, which overcome the hereinafore-mentioneddisadvantages of the heretofore-known products and processes of thisgeneral type and in which the liquid which can be produced in a simple,inexpensive manner and can be used as both an alkaline polishing liquidand an acidic polishing liquid.

[0011] With the foregoing and other objects in view there is provided,in accordance with the invention, an oxidizing polishing liquid forpolishing components, comprising a base polishing liquid and ozone (O₃).

[0012] The result is a polishing liquid with oxidizing properties whichcan be used to polish components, such as wafers or the like, and inparticular for the chemical mechanical polishing of components of thistype. Ozone is a strong oxidizing agent, the redox potential of which issufficient to polish the components in both an acidic environment and analkaline environment. Particularly if metal layers are to be polished,ozone is especially suitable for oxidizing the metals employed.

[0013] The polishing liquid according to the invention makes it possiblein principle to select any polishing liquid which may be suitable forthe particular application as the base polishing liquid, to which ozoneis then added. Since both the redox and the decomposition reactions ofozone take place without leaving any residues other than water andoxygen, special treatment of the waste water is not required.

[0014] Ozone is formed, for example in an ozone generator, from oxygenwith energy input according to Equation 1 below and has a decompositionreaction according to Equation 2:

2O₃←→3O₂   (Equation 1)

O₃→O₂+O,   (Equation 2)

[0015] wherein O represents atomic oxygen.

[0016] The way in which an ozonized polishing liquid according to theinvention acts for the polishing of metal layers can be represented ingeneral terms by the following Equations 3 to 6. First of all, the ozoneis reduced so as to form H₂O and O₂ in accordance with Equation 3

O₃+2H⁺+2e⁻→H₂O+O₂.   (Equation 3)

[0017] Furthermore, the atomic oxygen which is formed as a decompositionproduct of ozone is reduced in accordance with Equation 4

O+2H⁺+2e⁻→H₂O.   (Equation 4)

[0018] The oxidation of a metal Me^(o) which is to be polished to form ametal ion Me^(x+) takes place in accordance with Equation 5

Me^(o)→Me^(x+)+xe⁻.   (Equation 5)

[0019] Therefore, the above equations result in the following overallreaction for the action of the ozonized polishing liquid:

x/2O₃+xH⁻+Me^(o)→Me^(x−)+x/2H₂O+x/2O₂.   (Equation 6)

[0020] In preferred embodiments of the polishing liquid according to theinvention, the base polishing liquid is a colloidal solution of smallsolid particles in an alkaline medium having a pH greater than 7 or anacidic medium having a pH less than 7. Particularly suitable colloidalsolution polishing liquids include small solid particles of aluminumoxide, diamond, and/or silicon carbide. Colloidal solutions of suitablesmall solid particles are commercially available and can be selectedaccording to requirements and the particular application.

[0021] The oxidizing agent is advantageously ozone dissolved in water.

[0022] The ozone solution according to the invention has a redoxpotential of at least 2.0V in the acidic range, and preferably has aredox potential of approximately +2.075V.

[0023] Furthermore, the ozone solution according to the invention has aredox potential of at least 1.2V in the alkaline range, and preferablyhas a redox potential of +1.246V.

[0024] The redox potential of ozone is therefore sufficiently great tobe able to attack even metal layers which are difficult to oxidize, suchas, for example, copper or the like, in both the acidic and the alkalinerange. The redox potentials of customary oxidizing agents in aqueoussolutions compared to ozone are given in Table 1 below. TABLE 1 Redoxsystem Acidic solution Alkaline solution H₂O / O₃ +2.075 V +1.246 V H₂O/ O +2.422 V +1.594 V H₂O / H₂O₂ +1.763 V +0.867 V Fe²⁺ / Fe³⁺ +0.771 V−0.69 V Ce³⁺ / Ce⁴⁺ +1.72 V −0.7 V (SO₄)²⁻ / (S₂O₈)²⁻ +2.01 V +1.0 V

[0025] According to the invention, the quantity of ozone ranges fromabout 0.2 g to about 0.5 g.

[0026] This required quantity results from the fact that the solubilityof ozone in water is at most 49% by volume, corresponding toapproximately 1 g/l. It must be ensured that the dissolved quantity ofozone is sufficient to achieve the desired abrasion of metal. Themaximum required quantities of various oxidizing agents for completechemical conversion (i.e. oxidation) of 1 μm thick metal layers on 8inch wafers are given in Table 2 below. For an average polishing liquidconsumption of 500 ml per wafer to be polished, the maximum requiredquantity of ozone is as follows: TABLE 2 Metallic Oxidizing agentAluminum tungsten Copper Fe(NO₃)_(3/g) 2.47  5.19 2.33 (NH₄)₂Ce(NO₃)₈/g5.61 11.78 5.28 (NH₄)₂(S₂O₈)/g 1.17  2.45 1.10 H₂O₂/g 0.17  0.37 0.160₃/g 0.24  0.49 0.22

[0027] The polishing liquid according to the invention can be preferablyused for polishing, in particular for chemical mechanical polishing ofmetal layers and/or contact layers and/or adhesion layers of components,in particular wafers.

[0028] Such layers can be formed, in particular, of a material which isselected from the group consisting of aluminum, tungsten, copper,titanium, titanium nitride, tantalum and tantalum nitride. Of course,other metals can also be polished using the polishing liquid accordingto the invention.

[0029] According to the invention, the polishing liquid can be used forthe contact patterning and/or interconnect patterning of wafers.

[0030] With the above and other objects in view, there is also provided,according to a further aspect of the invention, a process for producinga polishing liquid for polishing components, preferably wafers, inparticular a polishing liquid according to the invention as describedabove, comprising the following steps:

[0031] a) providing a base polishing liquid comprising a colloidalsolution of small solid particles;

[0032] b) providing gaseous ozone as oxidizing agent; and

[0033] c) introducing the gaseous ozone into the base polishing liquid.

[0034] Through the use of the process according to the invention, it ispossible, in a simple and inexpensive manner, to produce a polishingliquid which can be used as both an alkaline and an acidic polishingliquid and which is particularly suitable for polishing metals. Withregard to the advantages, actions, effects and functioning of theprocess according to the invention, reference is hereby made to theabove statements relating to the polishing liquid and its use in theirentirety.

[0035] The ozone which is used as the oxidizing agent can initially beproduced as gaseous ozone in an ozone generator and can be added to thepolishing liquid at a suitable point. Corresponding installations formixing chemical solutions with ozone (also known as spiking) arecommercially available and can be positioned in the immediate vicinityof the polishing apparatus. Special installations for mixing and storingliquid in the vicinity of the polishing apparatus, as are required, forexample, in the prior art, can therefore be dispensed with. Existingcentral supply installations for polishing liquid can be retrofittedwithout any major structural outlay. In order to do this, it is merelynecessary to install an ozone generator and corresponding safety devicesand a metering unit. There is no need to repipe or add additional pipingto the central supply network.

[0036] Through the use of the present invention, the use of ozone asoxidizing agent first of all leads to a particularly advantageouspolishing liquid being formed. Furthermore, the ozone can be produced insitu and then added in the immediate vicinity of the polishingapparatus. Finally, it is possible to retrofit existing central supplynetworks without difficulty and without structural outlay.

[0037] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0038] Although the invention is illustrated and described herein asembodied in a polishing liquid for components, preferably wafers, aprocess for producing a polishing liquid and a process for chemicalmechanical polishing of components, it is nevertheless not intended tobe limited to the details shown, since various modifications andstructural changes may be made therein without departing from the spiritof the invention and within the scope and range of equivalents of theclaims.

[0039] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIGS. 1A and 1B are diagrammatic, partly sectional views of awafer which has been polished by using the polishing liquid according tothe invention; and

[0041]FIGS. 2A and 2B are diagrammatic, partly sectional views of afurther exemplary embodiment of a wafer which has been polished by usingthe polishing liquid according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Referring now to the figures of the drawings in detail and first,particularly, to FIG. 1A thereof, there is seen a wafer 10 which is toundergo chemical mechanical polishing by using an ozone-containingpolishing liquid according to the invention as described above. Thewafer 10 comprises a layer of silicon 11 as the base layer, in whichthere is a recessed metal layer 12. On the surface of the silicon layer11 and in a recess therein there is a tungsten layer 14, which is joinedto the silicon layer 11 and the metal layer 12 through a contact andadhesion layer 13.

[0043] In order to remove the excess tungsten, the wafer 10 ischemically mechanically polished using the ozone-containing polishingliquid. The resultant wafer configuration is illustrated in FIG. 1B. Ascan be seen from this figure, the residues of the tungsten layer 13which remain in the recess in the silicon layer 11 after conclusion ofthe polishing process form a contact 15, through which it is possible tomake contact with the metal layer 12 from outside the silicon layer 11.

[0044]FIGS. 2A and 2B show a further exemplary embodiment for thechemical mechanical polishing of a wafer 10. As can be seen inparticular from FIG. 2A, the wafer 10 once again comprises a siliconlayer 11 as the base layer in which there is a layer of metal 12. Analuminum layer 16 is disposed on the surface of the silicon layer 11 andin a recess in the silicon layer 11, through the use of a contact andadhesion layer 13. As an alternative to aluminum, it is also possible touse copper or the like, by way of example.

[0045] Through the use of the chemical mechanical polishing using theozone-containing polishing liquid according to the invention, thealuminum layer 16 on the surface of the silicon layer 11 is abraded.Parts of the aluminum layer 16 remain, as can be seen from FIG. 2B, butonly in the recess in the silicon layer 11. The remaining regions of thealuminum layer 16 form a contact/interconnect structure 17, throughwhich the metal layer 12 can be brought into contact with othercomponents inside and outside the wafer 10.

We claim:
 1. An oxidizing polishing liquid for polishing components,comprising a base polishing liquid and ozone.
 2. The polishing liquidaccording to claim 1 , including a colloidal solution of small solidparticles.
 3. The polishing liquid according to claim 2 , wherein saidsolution is alkaline.
 4. The polishing liquid according to claim 2 ,wherein said solution is acidic.
 5. The polishing liquid according toclaim 1 , wherein said ozone is dissolved in water.
 6. The polishingliquid according to claim 4 , including a redox potential of at least2.0 V.
 7. The polishing liquid according to claim 3 , including a redoxpotential of at least 1.2 V.
 8. The polishing liquid according to claim1 , wherein said ozone has a concentration range of from 0.2 g to 0.5 gper 500 ml of polishing liquid.
 9. The polishing liquid according toclaim 1 , wherein the component is a wafer.
 10. The polishing liquidaccording to claim 1 , adapted for chemical mechanical polishing.
 11. Aprocess for producing an oxidizing polishing liquid, which comprises thefollowing steps: a) providing a base polishing liquid having a colloidalsolution of small solid particles; b) providing gaseous ozone as anoxidizing agent; and c) introducing the gaseous ozone into the basepolishing liquid.
 12. The process according to claim 11 , wherein thebase liquid is alkaline.
 13. The process according to claim 11 , whereinthe base liquid is acidic.
 14. The process according to claim 11 , whichfurther comprises producing the ozone with an ozone generator.
 15. Aprocess for polishing components with a polishing liquid, whichcomprises: providing a polishing liquid having a base polishing liquidand ozone; and chemical mechanical polishing of components with thepolishing liquid.
 16. The process according to claim 15 , wherein thecomponents are wafers.
 17. The process according to claim 15 , whichfurther comprises polishing layers of a material selected from the groupconsisting of aluminum, tungsten, copper, titanium, titanium nitride,tantalum and tantalum nitride, with the polishing liquid.
 18. Theprocess according to claim 15 , which further comprises contactpatterning of wafers with the polishing liquid.
 19. The processaccording to claim 15 , which further comprises interconnect patterningof wafers with the polishing liquid.
 20. The process according to claim15 , which further comprises chemical mechanical polishing of at leastone of metal layers, contact layers and adhesion layers of componentswith the polishing liquid.